Abstract View
Fluid Mechanics and Droplet Transport from the Production of Unvoiced Fricatives
TANVIR AHMED, Andrea Ferro, Amir A. Mofakham, Brian T. Helenbrook, Goodarz Ahmadi, Deborah M. Brown, Byron D. Erath, Clarkson University
Abstract Number: 503
Working Group: The Role of Aerosol Science in the Understanding of the Spread and Control of COVID-19 and Other Infectious Diseases
Abstract
The COVID-19 pandemic has highlighted the importance of airborne droplet transport as an efficient vector for virus transmission. Recent work has identified how human speech produces droplet size distributions that are remarkably similar to coughing, and which are capable of staying suspended in aerosol form for long periods of time, thereby increasing infection risk. Missing, however, is a description of how these droplets are transported from the mouth exit, into the ambient environment. Although the time-averaged velocity at the exit of the mouth has been quantified for various English phrases, this prior work does not provide the temporal resolution that is needed to fully elucidate the highly transitory, unsteady fluid mechanics that are produced during human speech. This work identifies how specific utterances of speech (e.g., phones) are capable of producing unique fluid mechanics that are effective at transporting expirated droplets over distances that are longer than previous time-averaged measures have identified. Emphasis is placed on investigating the phones [f] and [θ], which are produced by the consonant production at the end of words such as “huff”, and “with”, respectively. These unvoiced fricatives are shown to produce a transient, high velocity jet of air at the mouth exit, due to the narrow constriction that is formed at the mouth during their pronunciation. The quantity and size distribution of human droplet production for these consonants are quantified and reported based on measurements using an aerodynamic particle sizer. Particle image velocimetry (PIV) of the velocity field at the exit of the mouth is also acquired from human intonations, as well as in physical models, to quantify the resultant jet momentum, elucidating how these transient speech behaviors entrain and advect droplets into the surroundings. These results are necessary for predicting infection risk from airborne viruses as a function of speaker distance.